The invention relates to coolant inhibitor compositions for use in fluid heat exchange systems predomninantly for, but not limited to, internal-combustion engines, and more particularly the invention relates to coolant inhibitor compositions which have an improved metal corrosion inhibitive function and an oxidative coolant deterioration inhibitive function leading to inhibition of corrosion of metal parts in heat exchange systems predominantly for, but not limited to, internal-combustion engines which may be otherwise caused by said oxidative coolant deterioration.
Most conventional heat exchange fluids for use in cooling systems for internal-combustion engines contain corrosion inhibitors such as phosphates, amine salts, silicates, borates, and/or nitrites to inhibit corrosion of various metal parts in the cooling system, however, such heat exchange fluids have shortcomings.
When a heat exchange fluid containing phosphates enters a river, lake, etc., the phosphates tend to increase BOD and/or COD levels therein, which can lead to proliferation of algae, which in turn can lead to the generation of hazardous pollutants.
Further, phosphates contained in a conventional heat transfer fluid tend to chemically react with hard water components coexisting in the fluid and form chemical depositions, which often lead to degradation of the corrosion inhibitive function of the fluid and can lead to plugging of the circulation passages in the heat exchange system.
Amine salts contained in a conventional heat exchange fluid can produce nitrosamines by chemically reacting with nitrites in the fluid or in another fluid when blended together in the cooling system. Nitrosamines are a carcinogenic substance.
Silicates contained in a conventional fluid are relatively unstable and have a tendency to polymerize when there are changes in temperature and/or pH values in the fluid and/or when other salts coexist, often leading to degradation of the corrosion inhibitive function of the fluid.
Borates contained in a conventional fluid tend to corrode aluminum and aluminum alloy parts of the heat exchange system.
Nitrites contained in a conventional fluid degrade quickly under actual use, therefore quickly degrading the corrosion inhibitive function of the fluid.
Japanese Patent Kokai (published unexamined) No. 2-182782/1990 discloses a heat exchange fluid which does not contain phosphates, amine salts, silicates, borates, or nitrites, but includes a C.sub.7 -C.sub.14 linear dicarboxylic acid and a triazole. The fluid has an improved metal corrosion inhibitive function and is relatively stable in hard water.
Said Japanese Patent Kokai No. 2-182782/1990, however, is not without a shortcoming. The aliphatic dibasic acid (linear-dicarboxylic acid) contained in said heat exchange fluid and aliphatic monobasic acids in general, which are widely used as metal corrosion inhibitors, gradually degrade the glycols used in the fluids by oxidation, resulting in a lowering the pH value of the fluid and in turn resulting in the promotion of corrosion of the metal parts in the heat exchange system.
Accordingly, it is an object of the present invention to provide heat exchange fluid compositions which possess an excellent metal corrosion inhibitive property, good stability in hard water and a long duration period in a cooling liquid, as well as an improved oxidation degradation inhibitive property.